Method of and apparatus for growing crystals from a solution

ABSTRACT

A mixture (liquid or solid), including a solvent, a solute (comprising the constituents of a crystal to be grown), and any desired dopant, is placed in a drum rotatable on a major (and preferably generally vertical) axis. Substrates are mounted in the drum above the mixture level. The mixture is heated to dissolve the solute and form a solution. The solution is moved over and covers the substrates via a centrifugally induced forced vortex by rotating the drum. The system is controllably cooled, or otherwise affected, to effect crystal growth on the substrate. Expedients are provided to accomodate substrates both denser than and less dense than the solution and to obviate undesirable effects of contaminants in the solution. Defects in the grown crystals caused by temperature gradients, solution concentration gradients and turbulence are also obviated by appropriate facilities.

United States Patent 1 1 Lien 1 1 Jan. 30, 1.973

[75] Inventor: Suei-Yuen Paul Lien, Morrisville,

[73] Assignee: Western Electric Company, Incorporated, New York, N.Y.

[22] Filed: May 27,1970

[2]] Appl. No.: 40,854

UNITED STATES PATENTS 3,033,159 5/1962 OBrien ..l17/101 X 3,097,1127/1963 Schutze et a1... ..117/101 X 3,212,929 10/1965 Pliskin et a1. 1 1..117/201 3,298,875 l/l967 Schink 1 ..117/106 X 3,429,295 2/1969 Shapiro..117/101 X Primary Examiner-Ralph S. Kendall Attorney-W. M. Kain, R. P.Miller and R. C. Winter 57 ABSTRACT A mixture (liquid or solid),including a solvent, a solute (comprising the constituents of a crystalto be grown), and any desired dopant, is placed in a drum rotatable on amajor (and preferably generally vertical) axis. Substrates are mountedin the drum above the mixture level. The mixture is heated to dissolvethe solute and form a solution. The solution is moved over and coversthe substrates via a centrifugally induced forced vortex by rotating thedrum. The system is controllably cooled, or otherwise affected, toeffect crystal growth on the substrate. Expedients are provided toaccomodate substrates both denser than and less dense than the solutionand to obviate undesirable effects of contaminants in the solution.Defects in the grown crystals caused by temperature gradients, solutionconcentration gradients and turbulence are also obviated by appropriatefacilities.

63 Claims, 14 Drawing Figures PAIENTEnmao 191a 3.713.883

sum nor 4 fiwmemam) 5 75 BACKGROUND OF THE INVENTION In an even morespecific sense, the present invention contemplates so called liquid.phase epitaxy (LPE),

vthat is, the controlled precipitation and epitaxial In all threemethods appropriate dopants (e.g., oxygen, zinc) may be used to causethe grown crystal compound to emit light of a predetermined wavelength.

First, the compounds may be grown by a non-epitaxial, bulk method from astochiometric or nearstochiometric melt, followed, if necessary, by zonerefining. Present melt-growth methods have been 1 found to be deficientfor a number of reasons. Among growth of single crystalline materialfrom a supersatu- Y rated solution onto a seed or substrate. Such singlecrystalline material may be a so-called Ill-V or lI-VI semiconductive,electroluminescent compound. However, as discussed subsequently, thepresent invention is not necessarily limited to the growth of only suchcompounds.

2. Discussion of the Prior Art semiconductive, electroluminescent diodesand other devices, for example those made of crystal compounds such asgallium phosphide [GaP] orgallium arsenid'e-phosphide [GaAs,,P, are themost efficient light sources known. Specifically, theelectroluminescence of these compounds is due to the band-gap energiesof their constituents being in the visible region of theradiationspect'rum. More specifically; electroluminescence is caused byexciton recombination mechanism or by direct band-gap electron holerecombination. Usually, the. constituents of an electroluminescentcompound arejselected as follows: I

' a. one or more element from column [ll ,of the Periodic Table one ormore elementlfrom Column V of the Periodic Table; or

these reasons are the necessity of high pressures (30-45 atm), hightemperatures (=l500" c), and elaborate facilities; the unwantedintroduction of impurities from crucibles at the pressures andtemperatures necessarily utilized; and the inability to consistentlygrow high quality crystals.

In a second method, the compounds may be grown by epitaxial growth viavapor transport. Present vapor transport growth methods produce, atrather slow rates, crystal compounds having electroluminescentefficiencies somewhat lower than compounds grown by other methods.

Third, the compounds may be grown from solutions (LPE). Specifically, aheated liquid-solvent phase of a solution (e.g., gallium) is used todissolve a solid-solute phase (e.g., gallium-phosphide). The desiredcompound is permitted to precipitate out either randomly or controllably(the latter being onto-a seed or substrate) by slowly lowering thetemperature of the solution (whicheffects supersaturation thereof) toprevent polycrystalline growth and to encourage single crystal growth.

b. one or more element from Column ll of the Periodic Table one or moreelement from Column VI of the Periodic Table.

Thus, in describing.electroluminescent compounds,

there are derived the terms Ill-V and ll-VI.

Further information concerning these compounds may be found in thefollowing references: Morpholo' gy of Gallium Phosphide Crystals Grownby VLS Mechanism with Gallium as Liquid-Forming Agent, by W. C. Ellis,C. J. Fros'ch and R. B. Zetterstrom in Journal Of Crystal "Growth,'2(1968), pages 61 68 (printed in the Netherlands); Visible Light fromSemiconductors, by MaxR; Lorenz in Science, Mar. 29,1968, Vol. 159,No.'3822, pages-14194423; and Solid State-Light" by A. S. Epstein and N.l-lolo'nyak in Science JournaL'January, 1969, pages 68-7 3. f

(Besides being efficient, electroluminescentdiodes and devices are moresturdy, reliable and longer-lived than, and are accordingly replacing,conventional incandescent lamps in a number of applications..Additionally, such diodes are compact, compatible with solid statecircuitry and require'very little power for operation. e

Nevertheless, difficulties have been experienced in rapidly,efficiently, and cheaply growing uniform, large area, single crystal,epitaxial compounds from which f Solution growth is potentially moredesirable than the other two prior art methods because it uses lowertemperatures "(901l00C) and lower pressures ambient), and producesstrain'free crystal diodes having the highest known electroluminescentefficiency (about 3XX higher than the first two methods). Solutiongrowth is rather slow (usually one-at-a-time), however, and has beenfound to often produce crystals having structural defects caused by,inter alia, solution concentration gradients, temperaturegradients,.turbulence and the capturing of undissolved dopants'in thegrown crystal. a,

.Thepresent invention, asnoted above,'is an improvement of the thirdprior art method, viz., the growth of crystalsfrorn a solution (LPE).Accordingly, another object of this invention is an improved method ofthe type last mentioned. v

As noted previously, the present invention is not limited to theepitaxial growth of single crystal, elecof, and a primary object of thisinvention, is the growth of crystals from a supersaturated solutionwhich contains a solvent and a solute, the crystals resulting fromcontrolled precipitati'on of the dissolved solute. I

A simple example of the type of crystal growth improved by the presentinvention may entail the growth of crystals of ordinary table salt.First, the table salt (the solute) is dissolved in a solvent therefor,such as water. If during the dissolutionof the salt, the water isheated, a saturated salt solution results upon addition of sufficientsalt. If, now, this saturated solution is cooled, supersaturationresults and the salt precipitates as solid, particulate crystallinematter. Such precipitation is generally random due to the generallyrandom location of nucleating sites, salt. concentration provided in thesolution, and if the thermal properties I and turbulence of the solutionare appropriately adjusted and-controlled, the salt will precipitate onand adhere to the substrate or seed. I

Methods similar to'the above-described precipitation of table salt arefound in prior art methods generally used to grow from solutionsepitaxial layers of semiconductor materials. Such a method is describedin U.S. Pat. application Ser. No. 556,192, filed June 8, 1966, andassigned to Bell Telephone Laboratories, lncorporated; and in U.S. Pat.No. 3,463,680. This method is usually referred to as the tipping method.

Specifically, in the tipping method of theprior art a graphite boat ispositioned in a tiltable furnace. A substrate or seed is held at one endof the boat, which is tilted to raise the substrate. The lowereddiametric side of the boat has placed therein a solution which includesa solvent (e.g., gallium), saturated with a solute (e.g., GaP) plus adopant, if desired.

The furnace-boat system is closed and the boat is heated to dissolve thesolute and the dopant. When the substrate and the solution reach anappropriate temperature, the boat is tipped to cover the substrate withthe heated solution. The temperatureis then controllably lowered both tosupersaturate the solution and to effect epitaxial deposition onto thesubstrate.

It should here be noted that the terms fseed and substrate are usedinterchangeably, the term seed" being the more genericterm.Specifically, a seed is defined as a single crystal ofa'material onwhich it is desired to grow a crystal. A substrate, on the other hand,is a slice of a seed. Thus, the only difference between the two terms istheir physical shape.

The above-described tipping method and methods derived therefrom are, atpresent, the best known methods of growing single crystal layers from asolution. As mentioned above, these methods are however, plagued withdifficulties which render them somewhat less than desirable.- v

' A first difficulty involves the inability of the prior art tippingmethods to effect the growth of single crystal epitaxial layerssimultaneously on a large numberof substrates or seeds; Specifically, asdescribed previously,epit'axial crystal growth involves the cooling of asaturated solution to a point where supersaturation ocours and thedesired material precipitates from the now supersaturated solution ontothe substrate or seed. Typically, prior art tipping methods have treatedone substrate at a time, which is most inefficient, and, of course,costly and slow. The reason for-one-at-a-time treatment is related inpart to difficult-to-analyze temperature gradients withinthe'super-saturated saturated solution when a large number of substratesare present. ln'view of the different cooling rates-of the solution andof a single substrate thereinafter tipping, the presence of numeroussubstrates generates many different temperature gradientsat differentpoints within the supersaturated solution. These temperature gradientsrender unpredictablethe' exact rate at which the desired crystalprecipitates the'refrom,that rate being temperature dependent. Moreover,these same gradients lead to a lack of a uniform substrate temperature.This, in turn results in the crystalline layers grown on the differentsubstrates varying in character from substrate to substrate. Anobject ofthe present invention is to eliminate these temperature gradientproblems in crystal growth.

A second difficulty with prior art crystal growth -tipping methodsrelates to the dopants which are often between the substrate-solventinterface making the grown crystalline layer either unacceptable orunpredictable in quality. Another object of this invention, then, is 'toeliminate such trapping of dopants and immundities inherent in prior artcrystal growing processes. i

A third problem involved in prior art tipping processes is related toso-called concentration gradients. Specifically, the substrate ismaintained at the bottom of or within the saturated solution as thesolutionis cooledto grow on the substrate the desired crystal. Suchgrowth is due to precipitation ,of the solute and'dopant from the cooledand now supersaturated solution. Such precipitation is not uniformthroughout the solution due to temperature gradients and mobilityconsiderations. Thus, precipitation generally first occurs from thatportion of the solution immediately adjacent 1 the substrate. Becausethis precipitation causes a depletion of the solute and dopant from suchportions of the-solution, the solute and dopant concentration in thatportion is decreased.

A decrease in the solute and dopant concentration in thesolution portionimmediatelyadjacent the substrate affects the density of that portion.Thatis', the density of thesolution portion may be rendered eithergreater or less than that of the rest of the solution.

The first situation is where the lower concentration portion of thesolution has a density greater than the remainder of the solution.Because all of the solute and dopant that can precipitate from thesupersaturated solution does precipitate from that portion of thesolution immediately adjacent the substrate, further precipitationcannot take place untilthc solution immediately adjacent the substratehas been replenished with the solute. Such replenishment may be effectedby stirring the solution. However, such stirring may cause thetemperature gradients in the solution to become non-uniform andrandomlylocated, thus, giving rise to the first problem of the tippingmethod discussed above. I

On the other hand, replenishment by naturaldiffusion may be allowed totake place. This, however, requires long time intervals making theprocess very slow and inefficient.

The second possibility, where a portion of the solution undergoes adensity change, is for that density to be less than that .of theremainder'of the solution. The less dense solution will tend to risegenerating either the temperature gradient problem or the turbulenceproblems discussed below.'-

Accordingly, yet another object of the present invention is to obviateconcentration gradient problems, such as described immediately above.

The fourth major difficulty with prior art crystal growing tippingprocesses is related to turbulence. Some of the difficulties caused byturbulence have been discussed previously. In addition, turbulenceimmediately adjacent the substrate is usually undesirable since itcauses variations in the thickness of (and the chemical and electricalcharacteristics of) the grown crystalline layer. It has been observedthat turbulence typically leads to striations in the grown crystallinelayers. Another object of this invention is to eliminate the turbulencedifficulties of the prior art methods.

Some workers in the art have attempted to eliminate the temperaturegradient problems in the following way: The substrate is positioned atthe bottom of a very deep solution mass. An appropriate temperaturegradient is then imposed on the system, the hope being that the largesolution mass will stabilize the thermal gradient. Such, however, hasnot been the case due to increased turbulence effects. Specifically,such increased turbulence is due to the so-called Rayleigh Numberexceeding 1700.

The Rayleigh, Number R is defined for the fluid-filled space between twoparallel horizontal places as where y coefficient of thermal expansionof the fluid;

0 -0 the temperature difference between the two I planes; a

g gravitational acceleration;

d= the separation between the planes;

v= kinematic viscosity of the fluid; and

K the thermal conductivity of the fluid.

Convection currents appear when R 1700.

As discussed below, LPE is best effected with the substrate positionedwithin the solution at the cold end of a thermal gradient therewithin.Thus, for LPE (O -0 may be quite large. As a consequence, all else beingequal, convection currents may be realistically eliminatedby minimizingthe d3 term. Obviously, the deep solution mass does just the opposite,i.e., it maximizes the d term. In fact convection cells have beenobservedwhen the deep solution mass is used. Such cells create theundesirable turbulence effects noted previously, e.g., striations in thegrown crystal layer. Moreover, rather than stabilizing the thermalgradient, the deep solution mass, in causing the convection cells,effects local temperature differences not only on a single substrate,but also from substrate to substrate, where several are used.Accordingly, another object of this invention is to prevent undesirableconvection cells by minimizing the Rayleigh Number in'an LPE process.

Typically, as noted above, it has been found desirable to locate thesubstrate at the colder end of the thermal gradient in the solutionbetween the substrate and the heat source. Specifically, the mostdesirable position for the substrate has been found to be one wherein asurface of the substrate, on which surface crystal growth is to takeplace, faces the heat source heating the solution, and is, therefore, atthe cold end of the temperature gradient within the solution betweenthat surface and the heat source. Such positioning enhances the growthof the epitaxial crystal in only one direction, namely, perpendicular tothe surface of the substrate. Effecting this optimum positioning of thesubstrate while eliminating the above prior art difficulties has, untilthis invention, proved impossible.

SUMMARY OF THE INVENTION With the above-mentioned and other objects inview, the present" invention contemplates a new and improved method ofand apparatus for growing crystals and more especially to a new andimproved method of and apparatus for epitaxially growing crystalsfrom 'asolution. I

In a preferred form of the present invention in its broadest aspects, asolvent and a solute are placed in a generally cylindrical drum orcontainer rotatable on a major axis. The solute comprises theconstituents of (and dopants in) a crystal which is to be grown, Alsoplaced in the drum, above the solution level therein, is a substrate ora plurality thereof.

The solvent and solute are heated to dissolve the solute (and dopants,if any) to form a solution. While the heat is maintained, the drum isrotated at aspeed sufficient to both move the solution up the side wallof the drum by centrifugal force in a so called forced vortex, and tohold the substrate against the side wall. Ultimately the substrate iscovered by the solution at which time the entire system is cooled. Suchcooling supersaturates the solution to effect the desired crystal growthon the substrate. When appropriate crystal growth is effected, rotationof the drum is' stopped and the solution falls to its natural levelbelow the substrate. In a first alternate embodiment, the substrateplaced within the drum is constrained against vertical movement andmovement parallel to the rotation of the drum, but is horizontallymovable, radially from the drum axis, between a first and a second stopmember. In this first embodiment heating is performed by, one of twoheat sources, namely, a first heat source outside of andsurrounding thedrum, or, a second heat source inside the drum and surroundedthereby.

The first external heat source is used when the substrate is less densethan the solution. Specifically, the rotation of the drum initiallyforces the horizontally movable substrate outwardly against the firststop member via centrifugal action. When the substrate is covered by thesolution (due to centrifugal force acting on the solution), thesubstrate floats thereon, i.e., it moves inwardly toward the drum's axisuntil it abuts the second stop members exposing to the solution thatsurface thereof which faces the heat source.

Accordingly, the exposed surface is ideally located, i.e., facing theheat source and at the cold end of the temperature gradient within thesolution between the surface and the heat source.

The second internal heat source is used when the substrate is denserthan the solution. Specifically, the rotation of the drum initiallyforces the horizontally movable substrate outwardly against the firststop member via centrifugal action. When the substrate is covered by thesolution, it remains against the first stop members exposing to thesurface that surface thereof which faces the heat source. Again, theideal location of the exposed substrate surface is effected.

A second alternative embodiment recognizes the presence of either denseror less dense immundities in the solution. Such immundities may be thedopant skin or scum, previously referred to, or may be other unwantedand undissolved immundities.

In the second alternative embodiment the drum is divided by acylindrical wall into an inner region and an outer annular region. Thetwo regions are interconnected for solution flow therebetween above thelevel of the solution which is put in the inner region. The substrateis'placed in the outer region in accordance with either the descriptionof the broader aspects of this invention, or of the firstalter'native'embodiment, above.

A heat sourceis energized. This heat source is one of the two typesdescribedabove. The drum is rotated to move the solution up the outerside wall of the inner region by centrifugal action in a first forcedvortex. Immundi'ties denser than the solution remain at the bottomthereof. lmmundi'ties less dense than the solution float on the solutionstopping their upward travel at some point below the interconnectionbetween the two regions as determined .by their density and therotational velocity of the drum.

After the solute isv dissolved in the solvent, the drum is rotated at aspeed sufficient to further move the solution up to the interconnection,whereupon the immuninvention which may be included with the apparatusdepicted in FIGS. 3, 4, SA, 58 and 6A-6F.

DETAILED DESCRIPTION Referring to FIG; 1 there is shown a product 20 ofthe type which is produced by the present invention.

The product 20 includes a crystal layer 21 grown by the method of thepresent invention on a substrate or seed crystal of, for example, aIII-V or a lI-VI electroludity-freesolution spills into the outerannular region.

Rotation of the drum continues until sufficient immundity-free solutionis present in the outer annular region to cover the substrates -by' asecond forced vortex. Crystal growth is effected, again, by cooling thesystem to supersaturate the solution. a

Other embodiments and modifications are discussed in detail below.

BRIEF 'DESCRIPT'IONOF THE DRAWINGS substrate or a seed in accordancewith the principlesof the present invention; 1

FIG. 2 is a stylized representation of the prior art tipping" method ofgrowing the crystal of FIG. 1, which prior art method is improved uponby the present invention; r

7 FIG. 3 is partially cross-sectioned elevation of apparatus by whichthe broadest aspects of the method of the present invention are effectedto grow the crystal layer shown in FIG. 1;

FIG. 4 illustrates a first alternative embodiment of the inventiondepicted in FIG. 3;

FIGS. 5A-5C are partial cross-sectional, elevational views illustratingthe apparatus of FIG. 3 as modified by FIG. 4 to carry out the firstalternative embodiment of the method of the present invention;

FIGS. 6-6F illustrate a second alternative embodiment of FIG. 3 as. wellas the various stages of the present method, which stages are alsocarried out by, but are not specifically'shown in connection with, theapparatus of FIGS. 3 4 and SA-SB;

FIG. 7 is-a partially cross-sectioned elevation of another embodiment ofapparatus usable in the present minescent compound appropriately doped.Typically, where the crystal layer 21 is an epitaxial,electroluminescent compound, the constituents of the layer 21 may begallium and arsenic [GaAs], gallium and phosphorus [GaP] or gallium,arsenic phosphorus [GaAs,P The present invention is not, however,intended to be limited to such compounds and, in fact, contemplates thegrowth of any crystal whether or not epitaxial or electroluminescent,which can be grown from a solution. v

Referring now to FIG. 2, stylized apparatus is shown for effecting theprior art tipping method of growing the crystal layer 21, for example agallium-phosphide [GaP] crystal layer, on the substrate 22 of FIGQl. Theprior art utilizes a furnace 23 tiltable from side-to-side on a pivot24. The furnace 23 is hea'table by any convenient heat source, such asthe RF coils 26, as shown. Included within the furnace 23'is a graphiteboat 28 having a convenient configuration.

One side of the boat 28 is provided with a substrate or seed holder 29of vany'conventional type. The substrate or seed 22 on which it isdesired to grow the crystal layer 21 is held at the bottom of the boat28 by the holder 29. I

In use, the furnace 23 .is tilted, for example, to the left, to lowerthe end 28a of the boat 28.which is diametrically opposite thesubstrate22 and the holder 29. Into this lowered end 280 of the boat 28are placed a solvent 30, such as a gallium solution, and a particulatesolute 31, which includes the constituents of the crystal to be .grownas well asany desired dopants. If the crystal layer 21 is to comprisegallium phosphide the particular matter will include gallium phosphidparticles. I

The furnace 23 is'sealed and the RF coils 26 are energized to heat thefurnace 23. Heating the furnace 23 aids in the dissolution of theparticulate matter 31' in the solvent 30. A sufficient excess ofparticulate matter 31 is included so that further heating eventuallyproduces a saturated solution 32. Next, the furnace 23 is tilted so thatthe heated saturated solution 32 flows over and covers the heatedsubstrate 22. The furnace 23 and, accordingly, the solution 32 and thesubstrate 22 is slowly and controllably cooled by appropriated controlof the RF coils 26. Such cooling, as previously described, effects thegrowth, epitaxial or otherwise, of the crystal layer 21 on the substrate22 by supersaturating the solution 32 and by precipitation of-the solutefrom the solution 32. v

The above-described prior art crystal growing method -.is plagued withnumerous difficulties and problems which have been-previously discussed.The apparatus of the present invention described immediately below isintended to obviate and eliminate all of the difficulties and problemsof the prior art.

Referring now to FIG. 3, there is shown 'novel apparatus 38 for carryingout the present process in its broadest aspects.

The apparatus. 38 includes a drum 40 located within a furnace 41 androtatable by any convenient means (not shown), as shown by the arrow 42,on a major axis 43 thereof. The axis 43 may conveniently be generallyvertically disposed. The drum 40 is heated by any convenient heatingmeans. Such heating means may include either a heat source, such as RFcoils 45 surrounding the exterior of the drum 40, or a heat source, suchas RF coils 46 located within a tube 47 surrounded by the drum 40. Bothheat sources 45 and 46 (and the tube 47) are generally coaxial with themajor axis 43 of the drum 40.

The drum 40 is partially filled with the solvent 30 and the particulatesolute 31 similar to the solvent and particulate solute used in theprior art and described above in the description of FIG. 2. Moreover,the solvent-particulate mixture 30 31 fills the drum 40 to someconvenient height H,.

Placed within the drum 40 in any convenient manner is at least onesubstrate 22, but preferably a plurality thereof. The substrates 22 maybe held in the drum 40 by J-shaped holders 50 at a minimum height Hgreater than the height P1,. The holders 50 may hold the substrates 22in either of the orientations shown in FIG. 3. Specifically, the holders50 may expose a first surface 51 of the substrates 22 by maintaining thesubstrates 22 against a side wall 52 of the drum 40. Alternatively, theholders 50 may expose a second surface 53 of the substrates 22 bymaintaining the substrates 22 against the tube 47 or against a radialextension 54 of the tube 47. In practice both of the holder arrangementsare not used at the same time and are shown in FIG. 3 only forconvenience. The I substrates 22 may be vertically stacked as shown, aslong as the relationship H l-I, obtains.

One of the heat sources 45 M46 is now energized depending on theorientation of the substrates 22. Specifically, the heat source 45 or 46energized is that heat source which directly faces the exposed substratesurfaces 51 which faces toward the major axis 43 and 53. If the firstsubstrate surface 51 is exposed, the internal heat source 46 isenergized; if the second surface 53 which faces away from the major axis43 is exposed, the external heat source 45 is energized.

. Energization of the appropriate heat source 45 or 46 heats thesolvent-solute mixture 30-31 and the substrates 22. Heatingis carriedout until the solvent-particulate mixture 30-31 and the substrates 22reach an appropriatetemperature and, if necessary, until the solvent 30is saturated with the solute 31 to produce the solution 32.

Next, the drum 40 is rotated as-shown by the arrow 42. Such rotationeffects the movement of the saturated solution 32 up the side wall 52 ofthe drum 40 by the action of centrifugal force. The rotational speed ofthe drum is selected so that ultimately the solution 32 assumes a forcedvortex configuration 55 shown in cross section by the dotted and dashedline. As is known forced vortices are paraboloid in cross section.

The solution 32 assumes the forced vortex configuration 55 and thesubstrates 22 are covered thereby, as shown, at an appropriaterotational velocity of the drum 40. While rotation of the drum 40continues, the heat source 45 or 46 is appropriately adjusted to beginslow cooling of the solution 32 and of the substrates 22. Such cooling,as described previously, supersaturates the solution 32 to effect thegrowth of the crystal layer 21 on the substrates 22 FIG. 1).

After the crystal layer 21 has been grown on the substrates 22, rotationof the drum 40 is stopped. In order to prevent further crystal growth,where such is not desired, a sudden stopping is used. Such stoppingeliminates the centrifugal force acting on the solution 32 and theforced vortex collapses. As such collapse occurs, the solution 32 runsdown the side wall 52 of the drum 40 to the bottom thereof at the height11,. Because H, is still less than H, all crystal growth ceases.

The above-described apparatus 38 eliminates the difficulties of theprior art crystal growing tipping processes. Specifically, the apparatus38 permits the simple and expeditious growth of the uniformlyv goodcrystal layers 21 on a large number of substrates 22 in a singleoperation. I

The heating sources 45 and 46 should bepreferably stationary because thedrum 40 rotates either within or around the energized heat sources 45 or46 respectively, the heating of both the substrates 2 and of thesolution 32 which has moved up the side wall 52 of the drum 40 issubstantially equal over the entire drum 40. That is, all of thesubstrates 22 and all portions of the solution 32'are exposed to theheat output of all the entire periphery of the heat source 45 or 46 asthe drum 40 rotates. Thus, an averaging or integration" of the heatinput to the various parts of the drum 40 takes place. In other words,the temperature gradient problem of the prior art is eliminated.Moreover, due to the fact that all of thesubstrates are maintained atthe same temperature, with respect to each other, the growth rate of thecrystal layer 21 on each substrate 22 is the same.

A second problem of the prior art eliminated by use of the apparatus 38relates to improperly dissolved or partially dissolved dopants and toother immundities present in the solution 32 (and in the solvent 30). Asdiscussed previously, the improperly or partially dissolved dopantsoften form a skin or a scum layer which may have a density greater thanor less than that of the solution 32. Moreover, other immundities in thesolution 32 may also havedensities greater than or less than that of thesolution 32.

, In FIGS. 6D and 6E is shown drum filled with solution 32 containingboth types of immundities, that is, those arising from undissolveddopants and those arising from other immundities and are represented byparticles 56a and 56b. For the purposes of discussing the behavior ofthe particles 56a and.56b, drum 70 of FIGS. 6D and 6E is equivalent todrum 40 of FIG. 3. The particles 56a are those particles or either typewhich are less dense than and, accordingly, float on the surface of thesolution 32 (and of the solvent 30). The particles 56b are thoseparticles of either type which are denser than and sink to the bottom ofthe solution 32 (and of the solvent 30). Upon rotation of the drum 70 asshown by the arrow 42 in FIG. 6E, the solution 32, as previouslydescribed, assumes the forced vortex configuration 55, that is, on andup the side wall 79 of the drum 70. .It has been found that theparticles 56a and 56b move -to definitely locatable positions upon suchrotation of the drum 40.

Specifically,.the denser particles 56b are thrown, by centrifugalaction, as is well known, against the bottom of the side wall 79 of thedrum 70. Depending upon the rotational velocity of the drum 70, thedenser particles 56b may tend to climb the side wall 79 in a mannersimilar to the solution 32; however, such rotational velocity may beempirically selected to insure that these particles 56b remain at ornear the bottom of the solution 32. k

The particles 56a which are less dense than the solu- I tion 32 havebeen found to continue to float on the solution 32 as that solutionassumes the forced vortex configuration 55. The average height H,, atwhich such particles 56a float on the solution 32 is easily empiricallydetermined and depends, inter alia, on such con ditions as both therelative densities of the particles 560 I and of the solution 32 andonthe rotational velocity of the drum-70. It has been found that'for agiven set of these conditions, the top of the forced vortex solutionconfiguration 55, will rise to a miximum height X but particles 56a.willrise only'tothe intermediate height I-I,,; Ultimately, if the height Hof the substrates 22' held by the holders 50 (as shown in FIG. '3) isselected to be greater than the'height H, and less than X, theimpurities 56a do not interfere with the growth of the crystal layer 21.Also, if it is desired to permit the-flow of that portion of thesolution through a passageway 73 (as shown in FIGS. 6A through7,particularly FIGS. 6C and 6F),"the position of the passageway 73should be at a height H, (FIGS, 6A) which is greater than the height H,but less than the height X.

Thus, the problems generated in prior art crystal growing processes byundissolved dopants or by other impurities are also obviated by the useof this invention.

Also, it has been found quite easy, using the apparatus 38 of FIG. 3, toeliminate the turbulence and convection cell problems of the prior art.Both of these problems are easily overcome due to the fact that theheight I-Iof the substrates 22 may quite simply be kept at a point wherethe thickness of a layer of the solution 32 in the forced vortex 55thereover is quite thinQThis thinness, as described earlier,minimizesthe d term. in the Rayleigh Number formula, thus eliminatingturbulence and convection cells. It is observed that near the top oftheparaboloid forced vortex 55, the layer of the solution 32 is quite thin.

As can thus be seen, the apparatus 38 of FIG. 3 properly effects thenecessary thermal gradient while expeditiously permitting the growth ona large number of substrates of uniform crystal layers. The thermal,turbulence, concentration and convection problems of the prior artarealso resolved at the same time.

Referring now to FIG. 4,. there is shown a firstalternative embodimentof the invention depicted in FIG. 3. While any convenient form ofsubstrate holder, such as the'J-shaped holders 50 ma'y be used, a holder57, as shown in FIG. 4 maybe preferred due to its versatility.

Specifically, the holder 57 may include the side wall 60 of theradialgextension 54 (shown in FIG. 3) of the tube-47 and the side wall52 of thedrum 40 defining an annular substrate-receiving groove 58therebetween. The holder 57 further comprises some convenient means,such as upper and lower annular screens 59 or other mesh-like or porousmaterial within-the groove 58. The screens 59 prevent vertical movementof the substrates 22. within the groove 58, but permit limited movementthereof between the surface 60 of the tube 47 and the side wall 52 ofthe drum 40. Thus, the tube surface 60 serves as a first stop member andthe drum side wall 52 serves as a second stop member. Any conventionalmeans, such as pairs of radial members 61, positioned about midwaybetween the screens 59, may

also be used in the groove 58 to limit movement of the favorablesubstrate orientation, viz., the surface 53 on substrates 22 parallel tothe direction of rotation of the drum 40.

The holder 57 is especially convenient, when a single embodiment, suchas the apparatus 38 of FIG. 3, is intended to be used with substrates 22which are either less dense than or denser than the solution 32. I

Specifically, assuming centrifugal action to have already filled thegroove 58 with the solution upon rotation of, the drum 40, a less densesubstrate floats on the solution 32 (which passes upwardly through thescreens 59) Such. floating forces the substrate 22 toward the axis 43and against the first stop member, i.e., the surface 60 of the tube 47to' expose the second substrate surface-53. Where'this is the case, theheat source utilized is the RF coils 45 exterior of the drum 40. Thusthere is effected the previously. described which the crystal layer 21is be to grown is at the cold end of the thermal gradient in thesolution 32.

A more dense substrate 22, on the other hand, is forced by thecentrifugal action away from the axis 43 and against the second stopmember, i.e., the sidewall 52 of the drum 40. In this position of thesubstrate 22, the first surface 51 thereof is exposed.- I-Iere, the heatsource 46'is used. Again the favorable substrate orientation in thethermal gradient is effected.

The substrate 22 does not, in reality, assume the position shown in FIG.4 (nor in FIGS. 68 and 7). Rather, as indicated by the double-headedarrow 62, the substrate 22, moves against either. the first or the Isecond stop member 60 or 52, respectively, depending on the densitythereof.

Referring now to FIGS. 5A and 58, there are shown two modificationsderived from the embodiments shown in FIGS. 3 and 4 and which embody theprincifurnace 41 is the heat source,which may comprise the ble from thedrum 40. The inside wall 65 of the member 64 and the outside surface 60'of the extension 54' define an annular, substrate-receiving compartment58' similar to the groove 58. The substrates 22 are held within thiscompartment 58' by any convenient means such as the'J-shaped holders 50,or more preferably a holder permitting the same limited substratemovement as the holder 57 of FIG. 4.

, Also asshown in FIG. SB the outside surface 60' of the extension 54may have, rather than a regular, annular configuration, a polygonalconfiguration such as an octagon. In this case the apexes of the octagoncontact the inside surface 65 of the member 64 to define a plurality ofsector-shaped compartments 58" which confine the substrates 22 in adirection parallel to the rotation of the drum 40. Here, the J-shapedholder 50 or the holder'57 may, of course, be used to constrain thesubstrates 22 vertically.

The bottom of the drum 40 includes a region 66 (FIGS. A and 5B)depressed below the bottom of the extension 54'. This depressed region66 includes a solution-containing well 67 into which either thesolventsolute mixture 30-31 or the saturated solution 32 is placed. Thedepressed region 66 communicates with the substrate-receivingcompartment 58 (or 58") via a plurality of holes 68 formed through thetongue-like member 63.

In operation, either the solvent-solute mixture 30-31 or the saturatedsolution 32 is placed in the well 66 and, as before, the RF coils 45maintain the system in a hightemperature condition until the solution 32results. Rotation of the drum 40 is initiated to cause, via centrifugalaction, the solution 32 to move out across the' bottom of the depressedregion 66 up through the holes 68 and into the compartment 58' or 58'.Ultimately, the substrates 22 within the compartment 58' or 58" arecovered by the solution 32. The RF coils 45 are then controlled to lowerthe temperature slowly, thus growing the crystal layers 21 on thesubstrates 22 as previously described. I

When proper crystal growth has been effected, the drum 40 is stopped,the solution 32 returning to the well 67 via the holes 68.

In the modification shown in FIG. 5A is assumed that the substrates 22are less dense than the solution 32. Accordingly, when that solutionfills the compartment 58' or 58" the substrates 22 float thereon andmove inwardly toward the axis 43 of the drum 40 and against the surface60 of the extension 54', which surface 60' serves as the first stopmember. Such movement exposes the second surface 53 of the substrates22. It is on this surface 53 that the crystal layer 21 is to be grown.Moreover, as shown in FIG. 5A if the substrates 22 are less dense thanthe solution 32, the heat source 45 exterior of the drum 40 is used.This positions the second surface 53 of the substrates 22 at the coldend of the thermal gradient existing in the solution 32 occupying thecompartment 58' or 58". The order of things 'as viewed from the drumaxis 43 is: the outside surface 60' of the extension 54', the substrates22, the second surface 53 thereof, the solution 32 within thecompartment 58' or 58" which covers the second surface 53, the insidewall 65 of the member 64, and the heat source 45. As previouslymentioned, this is the ideal location for the second substrate surface53.

The modification depicted in FIG. 5C is very similar to that of FIGS. 5Aand 5B with the exception that the heat source 46 located within thetube 47 is used. The reason for the use of heat source 46 is that thesubstrates 22 shown in FIG. 5C are denser than the solution 32.Accordingly, upon rotation of the drum 40 the solution 32 moves upthrough the holes 68 into the compartment 58' or 58". The densersubstrates 22 move against the surface 65 of the angled member 64exposing the first surface 51 thereof. Thus, the first surface 51 facesthe heat source 46. The order of things, then, as viewed from theexterior of the drum 40 is: the surface 65 of the member 64, thesubstrates 22, the first exposed surface 51 thereof, the solution 32covering the first surface 51, the outside surface of the extension 54and the heat source 46. ,Thus, again, the ideal location of the firstsubstrate surface 51, namely at the cold end of the thermal gradientwithin the solution 32, is effected.

I In the modification shown in FIGS. 5A5C any convenient form ofsubstrate holder may be used. To iterate, such holders preferably (butnot necessarily) permit generally horizontal movement of the substrates22 either toward or away from the axis 43 of the drum 40. The holdersshould, however, constrain the substrates 22 in the vertical directionand also in a direction parallel with the rotational movement of thedrum 40. Such a holder 57 is shown in FIG. 4 and may comprise themesh-like members, such as the screens 59, therein depicted.

It is apparent that the modifications of FIGS. 5A and 5C could be easilycombined by havingavailable for use both heat sources 45 and 46.Centrifugal action due to rotation of the drum 40 and/or the relativedensities of the substrates 22 and thesolution 32 position thesubstrates 22 against either the first stop member (the surface 60') orthe second stop member (the surface depending on the density of thesubstrate 22. Preknowledge of the density of' the substrates 22 thenpermits energizing the appropriate heat source depending upon whichsurface 51 or 53 of the substrates 22 will be exposed. I

Referring now to FIGS. 6A6F, there is shown a second alternativeembodiment of the present invention.

Contained within the furnace 41 is the drum 40 rotatable upon its majoraxis 43 as shown by the arrow 42. Both types of heat sources 45 and 46may be included depending upon the substrate density considerationsabove-described.

Within the drum 40 is a second drum generally coaxial therewith. Thedrums 40 and 70 thus define an inner region 71 and an outer annularregion 72. If the tube 47 is present within the drum 70 the inner region71 is also annular. If the tube 47 is not used, the inner region is not,of course, annular. The regions 71 and 72 intercommunicate via aplurality of passageways 73 formed through the wall of the drum 70. Thepassageways 73 are located at av height H, which is greater than theheight H, to whichthe less dense floating impurity particles 56a riseupon rotation of the drums 40 and 70, but is no higher than (and ispreferably lower than) a height X to which the solution 32 is able torise in the forced vortex configuration 55 (FIGS. 3 and 6E). Thefloating." of the particles 56a was described above in the descriptionof FIG. 3.

The substrates 22 are mounted within the outer an-' nular region 72 byany convenient means. Such mount ing means may (as in FIG. 5B) comprisesector-shaped compartments 58" or (as in FIGS. 3 and 6A) comprise theJ-shaped holders 50, previously described, which may hold the substrates22 against either the exterior wall 74 of the drum 70 (right-hand sideof FIG. 6A) or the outer, interior wall 75 of the drum 40 (left-handside of FIG. 6A). Preferably, the mounting means (as shown in FIG. 6B)comprises the type of holder 57 shown in FIG. 4. As described withreference to FIG..4'

the holder 57 permits horizontal movement of the substrates 22 butconstrains the substrates 22 vertically. and in a direction parallel tothe rotation of the drums 40 and 70. In this instance, if the holder 57is used, when the outer annular region 72 is filled with the'solution 32the substrates 22 (a) move inwardly toward the axis 43 against the wall74 of the drum 70 if they are less dense than the solution 32 and (b)move outwardly away from the axis 43 against the wall 75 of the drum 40if they are denser than the solution 32. Thus, the walls 74 and 75serve, respectively, as the first and second stop surfaces.

FIGS. 6A and 6D depict the situation prior to initiationof rotation ofdrums 40 and 70. FIG. 6D, as mentioned previously, shows the location ofimmundity particles 56a and 56b prior to rotation.

FIG. 6B shows an intermediate state in the process of this inventionwherein rotation of the drums 40 and 70 has been initiated and thesolution 32'has deformed into an intermediate forced'vortexconfiguration 55 tending toward the forced vortex configuration 55 shownin FIG. 3. As shown in FIG. 6B, the immundity particles 56a and 56bassume the positions previously described. It should be noted that theheight H, to which the'immundities 56a rise is below the height H, ofthe passages 73.

Accordingly, as shown in FIG. 6C, continued rotation of the drums 40 and70 causes the solution 32 to rise up to the passageways 73 and to beginflowing (numeral 76) therethrough into the outer annular region72.'Because of the location of the immundities 56a and 56b, as' shown inFIG. 6E, substantially immundity-free solution 32 passes into the outerannulai region 72.

Ultimately, as shown in FIG. 6F, the solution 32 in the outer annularregion 72 is moved up the inner wall 75 of the drum 40 by centrifugalforce into a second forced .vortex configuration 77. Such movement ofthe solution 32 covers the substrates 22 therewith. Moreover, if thetype of holder 57 depicted in FIG. 4 is used, either the first or thesecond surface 51 or 53 (see FIG. 6B), respectively, of the substrates22 will be.

covered by and exposed to the solution 32 within the outer annularregion 72, as indicated by the arrow 62 in FIG. 63. Control of theappropriate heat source 45 or 46 to cool the system is now effective togrow the crystal layer 21 on the substrates 22.

In the embodiment ofFIGS. 3 and 5A-5C, after the crystal layer 21 hadbeen grown, cessation of the rotation of the drum caused the solution 32to retreat from the substrates 22. In FIG. 3 the relation H I-I, isalways true; in FIGS. 5A-5C, the solution 32 returns to the well-67 viatheholes 68. In FIGS. 6A-6F either ap proach may be taken. As shown inFIG. 6F the height H of the lowest substrates may be chosenso that uponthe drums 40 and 70 stopping I-I I-I, where'H, is the height of thesolution 32 in theouter region '72.

On the other hand, as shown in FIG. 6C another approach maybe taken.Specifically, coaxially mounted to the drum 40 is a cup 90 defining anannular solution height and need not be greater than H, in the outerregion 72.

A modification of the second alternative embodiment of FIG. 6 isdepicted in FIG. 7. This modification is not limited to the apparatus ofFIG. 6, however, and may easily be adapted to the embodiments shown inFIGS. 3 and 5.

In the modification of FIG. 7 the substrates 22 are mounted by anyappropriate holder, such as the J- shaped holder 50 (left-hand side ofFIG. 7) or the holder 57 (right-hand side of FIG. 7 )within an annularchamber 77 "of a mesh-like cage 78. The cage 78 comprises a pair ofcoaxial mesh cylinders 80 and 81 defining the chamber and joined byamesh bottom 82. The cage bottom 82 contains a hole 83'large enough tofit over the drum 40.

The cage 78 is designed to fit into the outer annular region 72 and torotate along with the drums 40 and by any convenient means, for example,by a key-in-slot arrangement (not shown). The substrates 22 are loadedinto the chamber 77 of the cage 78 which initially resides in anupraised position as shown in FIG. 7. After such loading the cage 78 ismoved downwardly by means (not shown) into the outer outer annularregion 72, as shown by the arrows 84. Operation of the apparatus of FIG.7 then proceedsasin the description of FIGS. 6A-6F. After the crystallayers 21 have been grown on the substrates 22 the cage 78 is lifted outof the outer annular region 72, the substrates 22 being easilytransported without being contaminated within thecage78. Where theholder 57 is used, the walls of the cylinders and 81 serve,respectively, as the first and second stop members. l

The cage 78 may, accordingly, be viewed either as a handling expedient,as an alternative to, the passageway-valve-receptacle 92-93-91arrangement of FIG. 6C (upward movement of the cage 78 may terminatecrystal layer growth notwithstanding the relation ofH to IL), or both.

Thus, there has been described a method, and apparatus for effectingthat method, which method permits the convenient growth of crystallayers of any type from a solution on'one or on a plurality ofsubstrates simultaneously while eliminating all of the difficulties ofprior art processes and apparatus. It should be noted that theabove-described embodiments of this crystal growing-method aresimplyillustrative of the principles of the present invention. Numerousother arrangements and modifications may be devised'by one skilled inthe art without departing from the spirit and scope of this invention.For example, the forced vortex 55 may be generated by an impellerarrangement (not shown) within and generally coaxial with either of thedrums 40 and 70. Such impeller arrangement may be similar to theimpeller of a centrifugal pumpor of a conventional cream separator. 1

Moreover, it is not necessary that the forced vortex 55 be generatedsimultaneously with the cooling of the saturated solution 32.Specifically, as described previously, if the saturated solution 32 iscooled to the point of super-saturation without the substrate or seedbeing present, solid, particulate crystalline matter randomlyprecipitates therein. If the seed or substrate 22 is present in thesolution 32 at supersaturation, the crystal layer 21 is grown thereon.Many saturated solutions 32 have been'found to possess a propertywhereby the temperature at which random precipitation occurs is lowerthan the temperature at which the controlled growth of the crystal layer2l occurs. Accordingly, the present invention may be used in thefollowing manner: The particulate solute 31 is dissolved in the solvent30 at an elevated temperature to produce the saturated solution 32. Thesaturated solution 32 is then cooled to a point where supersaturationoccurs but the random precipitation does not occur. The substrate 22 isnext placed in the drum 40 and is maintained at a temperature at whichcrystal growth thereon will take place. The forced vortex configuration55 may now be imposed on the supersaturated solution so that thesubstrate 22 is at least momentarily covered thereby.

Growth of the crystal layer 21 occurs.

In order that those skilled in the art may more fully understand theinventive concept herein present, the following examples are given byway of illustration and not limitation.

EXAMPLE I Apparatus similar to that illustrated in FIG. 5A was employed.The apparatus comprised an ultra-pure graphite drum 40 and an ultra-puregraphite tube 47. A suitable p-type doped GaP substrate 22, grown bystandard liquid encapsulated pulling techniques and cut to size, wasselected. Thesubstrate 22 was placed within a substrate-receivingcompartment 58 of the apparatus, defined by the inside wall 65 of member64 and the outside surface 60' of extension 54' of the tube 47 A galliumGaP Ga O Zn mixture 30-31 was prepared by weighing out 0.931 mole ofhigh purity gallium, 0.0015 mole of zinc, 0.0035 mole of Ga o and 0.064mole GaP. The resultant mixture 30-31 was placed in a well 67 of region66 of the apparatus. The amount of Ga? present in the mixture 30-31 wassuch as to give a GaP saturated gallium solution doped with oxygen andzinc at a temperature of l050 C. An ambientatmosphere of argon wasmaintained within drum 40 and furnace 41 of the apparatus and thefurnace 41 was heated, by means of RF coils 45, to the temperature of1050" C, thereby forming the Gal saturated gallium solution 32.

When the temperature of,l050 C was reached, the drum 40 was rotated, byconventional means, at a rate of 750 to 850 revolutions/minute. Therotation of the drum 40 caused, via centrifugal force, or action, thesolution 32 to move into compartment 58 and cover the substrate 22.Crystal growth was then initiated by lowering the temperature ata rateof 100 C/minute. Upon reaching a temperature at 700 C the spinning wasstopped, thereby terminating the crystal growth. Theapparatus was cooledto room temperature and the substrate 22 was removed. I

An epitaxial layer having a thickness of about lp.m was obtained. Thethickness uniformity obtained was 18 good, as evidenced by a Taly-Surfmeasured central line average of0.5p.m.

EXAMPLE II The procedure of Example I was repeated except that therotation was at a rate of 850 to 950 revolutions/minute, and therotation was terminated at a temperature of 750 C. An epitaxial layer ofabout p.m was obtained having a central line average of l.0p.m.

What is claimed is: 1. In a method of growing a crystal layer on asubstrate from a liquid body rich in the constituents of the layer,which method includes at least a step of contacting the substrate withthe liquid, the improvement comprising:

' configurating the liquid body in a forced vortex to effeet thecontacting where the distance between the substrate and the free surfaceof said forced vortex is such that the Rayleigh Number is less thanabout 1700. I

.2. In a method of growing a crystal layer on a selected portion of asubstrate from a liquid body rich in the constituents of the layer theimprovement comprising:

configurating the liquid body in a forced vortex; and

contacting the selected substrate portion with said forced vortex, thedistance between the substrate portion and the free surface of saidforced vortex during said contacting being such that the Rayleigh Numberis less than about 1700.

3. The method of claim 2 which includes the further step of: I

positioning the substrate in a container and wherein said configuratingstep includes,

placing the liquid body in said container,.and

rotating the container.

4. The method ofvclaim 3 wherein during said contacting step therotational velocity of said container during said contact is a velocityat which the distance between the selected substrate portion and thefree surface of said forced vortex is such that the Rayleigh Numberwithin said distance is less than about 1700.

' 5. The method of claim 4 wherein said contacting step iseffected as aconsequence of the effectuationof said configurating step.

6. In a method of growing a crystal layer on at least a portion of aselected surface of a substrate in a container from a solution rich in asolute of the crystals constituents wherein (i) a solvent in thecontainer out of contact with the substrate is saturated at anelevatedtemperature with the solute to produce the solution, (ii) the selectedsubstrate surface is contacted with the solution, and (iii) the solutionis cooled to a supersaturated condition, the improvement comprising:

imposing on the solution a forced vortex configuration which contactsthe selected substrate surface portion to effect step (ii), the distancebetween the portion of the selected surface and the free surface of saidforced vortex during step (ii) being such that the Rayleigh Number isless than about 1700. 7. The method of claim 6 wherein said forcedvortex is imposed on the solution by rotating the container.

8. The method of claim 7 wherein the rotational velocity of thecontainer during said contact is a velocityat which the distance betweenthe selected substrate surface portion and the free surface of saidforced solution vortex, measured generally perpendicular to saidselected substrate surface is such that the Rayleigh Number with saiddistance is less than about 1700.

9. In a method of growing a crystal layer on a selected surface of asubstrate in a container from a solution rich in a solute of thecrystals constituents wherein (i) a solvent in the containerout ofcontact with the substrate is saturated at an elevated temperature withthe solute to produce the solution, (ii) the selected substrate surfaceis contacted with the solution, and (iii) the solution is cooled to asupersaturated condition, the improvement comprising:

generating a forced vortex of the solution, which solution vortex coversthe selected substrate surface to effect step (ii), the distance betweenthe selected substrate surface and thefree surface of said forced vortexduring step (ii) being such that the Rayleigh Number is less than about1700.

10. The method of claim 9 wherein said forced vor tex is generated byrotating'the container.

11. The method of claim 10 wherein the rotational velocity of thecontainer during said contact is a velocity at which the distancebetween the selected substrate surface and the free surface of saidforced solution vortex, measured generally perpendicular to saidselected substrate surface is such that the Rayleigh Number within saiddistance is less than about 1700.

12. In a method of growing a crystal layer on a substrate in acontainer. from a solution rich in a solute of the crystals constituentswherein (i) a solvent in the container out of contact with the substrateis saturated at an elevated temperature with the solute to produce thesolution, (ii) the substrate is contacted by the solution, and (iii) thesolution is cooled until supersaturation occurs, the improvementcomprising:

rotating the container on a symmetrical axis thereof until the solutionis moved in a forced vortex which contacts the substrate in such amanner that the distance between the substrate and the free surface ofsaid forced vortex during step (ii) leads to a Rayleigh Number which isless than about t 1700. 13. The method of claim 12 wherein step (iii) iseffected after step (ii).

14. The method of claim fected before step (ii).

15. The method of claim 12 wherein steps (ii) and (iii) are effectedsimultaneously.

16. The methodo'f claim 12 which the step of;

effecting relative movement between-said forced 12 wherein step (iii) iseffurther includes solution vortex and the substrate for terminating thecontact therebetwee'n to terminate the growth of the crystal layer. l7.The'method ,of claim movement is effected by:

stopping said container rotation for effecting the collapse of saidforced vortex.

18. The method of claim 12 wherein: said container is drum-like and,rotatable on said axis which is generally vertical and includes a sidewall generally coaxial with said axis, and wherein said rotation iseffected generally horizontally about said axis.

16 wherein said relative 19. The method of claim 18 wherein therotationalvelocity of said drum-like container during said contact is avelocity at which the distance between the substrate and the freesurface of said forced vortex is such that the Rayleigh Number is lessthan about 1700.

20. The method of claim 19 wherein the solution contains immunditieshaving densities greater than or less than the solution and wherein therotational velocity of said drum-like container during said contact is avelocity at which the denser immundities remain at the bottom of thecontainer and the less dense immundities float on said forced vortex outof contact with the substrate.

21. The method of claim 18 wherein the solution contains immunditieshaving densities greater than or less than the solution and wherein therotational velocity of said drum-like container during said contact is avelocity at which the denser immundities remain at the bottom of thecontainer and the less dense immundities float on said forced vortex outof contact with the substrate.

22. The method of claim 18 which further includes the step of:

positioning the substrate within said drum-like container to beconstrained against vertical movement and radially movable horizontallytoward and away from said axis between a first and a second stop member,respectively.

23. The method of claim '22 in which the substrate is less dense thanthe solution and effectuation of the rotating step further includes:

contacting the substrate with the solution to move the substrate towardsaid axis and against said first stop member to expose a first surfacethereof facing away from said axis and to impinge the solution on saidfirst surface.

24. The method of clairn'23which further includes the step of isurrounding the exterior of said drum-like container with a first sourceof heat flux generally coaxial with said axis to orient said firstsurface at the cold end of the thermal gradient within the solutionbetween sad first heat flux source and said first surface.

25. The rnethod of claim 22 in which the substrate is denser than thesolution and effectuation of the rotating step further includescontacting the substrate with the solution to move the substrate awayfrom said axis and against said second stop member to expose'a secondsurface thereof facing toward said axis and to impinge the solution onsaid second surface.

26. The method of claim 25 which further includes the step of:

surrounding a second source of heat flux with said drum-like container,said second heat flux source being generally coaxial with said axistolorient said second surface at the cold end of the thermal gradientwithin the solution between said second heat flux source'and said secondsurface.

27. In a method of growing a crystal layer on a substrate from a heated,saturated solution rich in a solute made up of the crystalsconstituents, which method includes contacting the substrate with thesolution, the solution including immundities having densities greaterthan or less than the solution, the improvement comprising: i

a. placing the solution in an inner, fluid-receiving region of a drumrotatable on a major axis, the drum further including an outer annularregion, both regions including side walls generally coaxial with saidaxis and interconnected at a position above the level of the solutionwithin said inner region;

. positioning at least one substrate within said outer annular region;

c. rotating said drum until centrifugal action moves the solution in afirst forced vortex up said side wall of said inner region, through saidinterconnection, and into said outer annular region, to contact thesubstrate with a second forced solution vortex, such that the distanceof the substrate and the free surface of said second forced solutionvortex dur-' ing said contacting is one whereby the Rayleigh Number isless than about 1700, the denser immundities remaining at the bottom ofthe solution in said inner region, the less dense immundities floatingon said first forced solution vortex at a level below said.interconnection; and d. cooling the solution to effect growth of thecrystal layer on the substrate by supersaturating the solution. 28. Themethod of claim 27 wherein step (b) includes: I

positioning the substrate within said outer annular region so'that thesubstrate is constrained against vertical movement and is radiallymovable horizontally toward and away from said axis between a firstand asecond stop member, respectively. 29. The method of claim 28 in whichthe substrate is less dense than the solution and effectuation of step(c) further includes:

contacting the substrate with the solution to move the substrate towardsaid axis and against said first stop member to expose a first surfacethereof fac- -ing away from said axis and to impinge the solution ofsaid second forced vortex on said first surface. 30. The method of claim29 which further includes the step of: v

surrounding the exterior of said drum with a first source of heat fluxgenerally coaxial with said axis to orient said first surface at thecold end of the thermal gradient within said second forced solutionvortex between said first heat source and said first surface. p 31. Themethod of claim 28 in which the substrate is denser than the solutionand effectuation of step (c) further includes:

contacting the substrate with the solution to move the substrate awayfrom said axis and against said second stop member to expose a secondsurface thereof facing toward said axis and to impinge the solution ofsaid second forced vortex on said second surface. 32. The method ofclaim 31 which further includes the step of:

surrounding a second source of heat flux with said drum, said second.heat source being generally coaxial with said axis, to orient saidsecond surface at the cold end of the thermal gradient within said Isecond forced solution vortex between said second heat source and secondsurface.

selected surface ofthe substrate in a container from a supersaturatedsolution containing the constituents of the layer, the improvementcomprising:

forming the solution by centrifugal force into a forced vortex havingan-immundity-free substrate contacting layer. I

35. A method of growing a crystal layer on a selected portion of asubstrate from a liquid body, rich in the constituents of the layer, theimprovement comprising:

configurating the liquid body in a forced vortex, and contactingtheselected substrate portion with said forced vortex such that anyimmundities present in the liquid body lie without a region bounded bythe distance between the selected substrate portion and said forcedvortex. i 36. The method of claim 35 which includes the further step of:

positioning the substrate in' a container and wherein said configuratingstep includes: placing the liquid body in saidcontainer, and rotatingthe container. A 37. The method of claim 36 wherein during saidcontacting step the rotational velocity of said container during saidcontact is a velocity at which the distance between the selectedsubstrate portion and the free surface of said forced vortex is suchthat'the Rayleigh Number within said distance is less than about 1700.

38. The method of claim 37 wherein said contacting step is effected as aconsequence of the effectuation of said configurating step.

39. in a method of growing a crystal layer'on at least a portion of aselected surfaceof a substrate in a container from a solution rich in asolute of the crystals constituents wherein (i) a solvent in thecontainer out of contact with the substrate is saturated at an elevatedtemperature with the solute to produce the solution, (ii) the selectedsubstrate surface is contacted'with the solution, and (iii) the solutionis cooled to a supersaturated condition, the improvement comprising:

imposing on the solution a forced vortex configuration which contactsthe-selected substrate surface portion to effect step (ii) in such amanner that any immundities contained in the solution lie without aregion bounded by the distance between the selected surface and the freesurface of said forced vortex. 40. The method of claim 39 wherein saidforced vortex is imposed on the solution by rotating the container. 41.The method of claim-40 wherein the rotational velocity of the containerduring said contact is a velocity at which the distance between theselected substrate surface portion and the free surface of said forcedsolution vortex, measured generallyperpendicuselected substrate surfaceis contacted with the solu-' tion, and (iii) the solution is cooled to asupersaturated condition, the improvement comprising:

generating a forced vortex of the solution to cover the selectedsubstrate surface therewith to effect step (ii) in such a manner thatany immundities contained in the solution lie without a region boundedby the distance between the selected substrate surface and the freesurface of said forced vortex.

43. The method of claim 42 wherein said forced vortex is generated byrotating the container.

44. The method of claim 43 wherein the rotational velocity of thecontainer during said contact is a velocity at which the distancebetween the selected substrate surface and the freesurface of saidforced solution vortex, measured generally perpendicular to saidselected substrate surface is such that the Rayleigh Number without saiddistance is less than about 1700.

45.ln a method of growing a crystal layer on a substrate in a containerfrom a solution rich in a solute of the crystals constituents wherein(i) a solvent in the container out of contactwith the substrate issaturated at an elevated temperature with the solute to produce thesolution, (ii) the substrate is contacted by the solution, and (iii)the'solution is cooled until supersaturation occurs, the improvementcomprising:

rotating the container on a symmetrical axis thereof at a sufficientrotational velocity to (1) move the solution in a forced vortex whichcontacts the substrate to effect step (ii), (2) effect retention atthebottom of the containerof any immundities having a density greater thanthe solution and (3) effect a floating on said forced vortex out ofcontact with the substrate of any immundities having a density less thanthe solution.

v46. The method .of claim 45 wherein step (iii) is effected after step(ii). 5

. 47,Th'e method of claim .45 wherein step (iii) is ef fected beforestep (ii).

48. The method of claim '45 wherein step (ii) and (iii) are effectedsimultaneously.

49. The method-of claim 45-which further includes the step of:

effecting relative movement between said forced solution vortex and thesubstrate for terminating the contact therebetween to terminate thegrowth of the crystal layer.

50. The method of claim 49 wherein said relative movement is effectedby: n

stopping said container rotation for effecting the lapse of said forcedvortex. I

5 L-The method of claim"45 wherein:

said container is drum-like and rotatableon said axis which is generallyvertical and includes a side wall generally coaxial with said axis, andwherein col- ' the container, of:

said rotation is effected generally horizontally about said axis.

52. The method of claim 51 wherein the rotational velocity of saiddrum-like container during said contact is a velocity at which thedistance between the substrate and the free surface of said forcedvortex is such that the Rayleigh Number is less than about 1700.

53.. The method of claim 51 which further includes the step-of:

' positioning the substrate within said drum-like container to beconstrained against vertical movement and radially movable effectuationtoward and away from said axis between a first and a second stop member,respectively.

54. The method of claim 53 in which the substrate is less dense than thesolution and effectutation of the rotating step further includes:

contacting the substrate with the solution to move the substrate towardsaid axis and against said first stop member to expose a first surfacethereof facing away from said axis and to impinge the solution on saidfirstsurface.

55. The method of claim 54 which further includes the step of:

surrounding the exterior of said drum-like container with a first sourceof heat flux generally coaxial with said axis to orient said firstsurface at the cold end of the thermal gradient within the solutionbetween said first heat flux source and said first surface.

56. The method of claim 53 in which the substrate is denser than thesolution and effectuation of the rotating step further includes:

contacting the substrate with the solution to move the substrate awayfrom said axis and against said second stop member to expose a secondsurface thereof facing toward said axis and to impinge the solution onsaid second surface.

57. The method of claim 56 which further includes surrounding a secondsource of heat flux with said drum-like container said second heat fluxsource being generally coaxial with said axis to orient said secondsurface at the cold end of the thermal gradient within thesolutionbetween said second heat flux source and said second surface.

58. In a method of growing a crystal layer on a substrate from a heated,saturated solution rich in a solute made up of the crystalsconstituents,which method includes contacting the substrate withthesolution, the solution including immundities having densities greaterthan or less than the solution, the improvement comprising: v

a. placing the solution in an inner, fluid-receiving region of a drumrotatable on a major axis, the drum further including an outer annularregion, both regions including side walls generally coaxial with saidaxis and interconnected at a position above the level of the solutionwithin said innerregion; positioning at least one substrate within saidouter annular region; rotatingsaid drum until centrifugal action movesthe solution in a first forced vortex up said side wall of said innerregion, through said interconnection, and into said outer annularregion, to contact the substrate with a second forced solution vortex,the denser immundities remaining at the bottom of the solution in saidinner region, the less dense immundities floating on said first forcedsolution vortex at a level below said interconnection; and d. coolingthe solution to effect growth of the crystal layer on the substrate bysupersaturating the solution. I 59. The method of claim 58 wherein step(b) includes:

positioning the substrate within said outer annular region so that thesubstrate is constrained against vertical movement and is radiallymovable horizontally toward and away from said axis between a first anda second stop member, respectively. 60. The method of claim 59 in whichthe substrate is less densethan the solution and effectuation of stepfurther includes:

contacting the substrate with the solution to move the substrate towardsaid axis and against said first stop member to expose a first surfacethereof facing away from said axis and to impinge the solution of saidsecond forced vortex'on said first surface. 61. The method of claim 60which further includes the step of:

surrounding the exterior of said drum with a first source of heat fluxgenerally coaxial with said axis to orient said first surface at thecold end of the thermal gradient within said second forced solutionvortex between said first heat source and said first surface. r 62. Themethod of claim 59 in which the substrate is denser than the solutionand effectuation of step (c) further includes:

contacting the substrate with the solution to move the substrate awayfrom said axis and against said second stop member to expose a secondsurface thereof facing toward said axis and to impinge the solution ofsaid second forced vortex on said second surface. 63. The method ofclaim 62 which further includes the step of:

surrounding a second source of heat flux with said drum, said secondheat source being generally coaxial with said axis, to orient saidsecond surface at the cold end of the thermal gradient within saidsecond forced solution vortex between said second heat source and saidsecond surface.

' I Eli

1. In a method of growing a crystal layer on a substrate from a liquidbody rich in the constituents of the layer, which method includes atleast a step of contacting the substrate with the liquid, theimprovement comprising: configurating the liquid body in a forced vortexto effect the contacting where the distance between the substrate andthe free surface of said forced vortex is such that the Rayleigh Numberis less than about
 1700. 2. In a method of growing a crystal layer on aselected portion of a substrate from a liquid body rich in theconstituents of the layer the improvement comprising: configurating theliquid body in a forced vortex; and contacting the selected substrateportion with said forced vortex, the distance between the substrateportion and the free surface of said forced vortex during saidcontacting being such that the Rayleigh Number is less than about 1700.3. The method of claim 2 which includes the further step of: positioningthe substrate in a container and wherein said configurating stepincludes, placing the liquid body in said container, and rotating thecontainer.
 4. The method of claim 3 wherein during said contacting stepthe rotational velocity of said container during said contact is avelocity at which the distance between the selected substrate portionand the free surface of said forced vortex is such that the RayleighNumber within said distance is less than about
 1700. 5. The method ofclaim 4 wherein said contacting step is effected as a consequence of theeffectuation of said configurating step.
 6. In a method of growing acrystal layer on at least a portion of a selected surface of a substratein a container from a solution rich in a solute of the crystal''sconstituents wherein (i) a solvent in the container out of contact withthe substrate is saturated at an elevated temperature with the solute toproduce the solution, (ii) the selected substrate surface is contactedwith the solution, and (iii) the solution is cooled to a supersaturatedcondition, the improvement comprising: imposing on the solution a forcedvortex configuration which contacts the selected substrate surfaceportion to effect step (ii), the distance between the portion of theselected surface and the free surface of said forced vortex during step(ii) being such that the Rayleigh Number is less than about
 1700. 7. Themethod of claim 6 wherein said forced vortex is imposed on the solutionby rotating the container.
 8. The method of claim 7 wherein therotational velocity of the container during said contact is a velocityat which the distance between the selected substrate surface portion andthe free surface of said forced solution vortex, measured generallyperpendicular to said selected substrate surface is such that theRayleigh Number with said distance is less than about
 1700. 9. In amethod of growing a crystal layer on a selected surface of a substratein a container from a solution rich in a solute of the crystal''sconstituents wherein (i) a solvent in the container out of contact withthe substrate is saturated at an elevated temperature with the solute toproduce the solution, (ii) the selected substrate surface is contactedwith the solution, and (iii) the solution is cooled to a supersaturatedcondition, the improvement comprising: generating a forced vortex of thesolution, which solution vortex covers the selected substrate surface toeffect step (ii), the distance between the selected substrate surfaceand the free surface of said forced vortex during step (ii) being suchthat the Rayleigh Number is less than about
 1700. 10. The method ofclaim 9 wherein said forced vortex is generated by rotating thecontainer.
 11. The method of claim 10 wherein the rotational velocity ofthe container during said contact is a velocity at which the distancebetween the selected substrate surface and the free surface of saidforced solution vortex, measured generally perpendicular to saidselected substrate surface is such that the Rayleigh Number within saiddistance is less than about
 1700. 12. In a method of growing a crystallayer on a substrate in a container from a solution rich in a solute ofthe crystal''s constituents wherein (i) a solvent in the container outof contact with the substrate is saturated at an elevated temperaturewith the solute to produce the solution, (ii) the substrate is contactedby the solution, and (iii) the solution is cooled until supersaturationoccurs, the improvement comprising: rotating the container on asymmetrical axis thereof until the solution is moved in a forced vortexwhich contacts the substrate in such a manner that the distance betweenthe substrate and the free surface of said forced vortex during step(ii) leads to a Rayleigh Number which is less than about
 1700. 13. Themethod of claim 12 wherein step (iii) is effected after step (ii). 14.The method of claim 12 wherein step (iii) is effected before step (ii).15. The method of claim 12 wherein steps (ii) and (iii) are effectedsimultaneously.
 16. The method of claim 12 which further includes thestep of; effecting relative movement between said forced solution vortexand the substrate for terminating the contact therebetween to terminatethe growth of the crystal layer.
 17. The method of claim 16 wherein saidrelative movement is effected by: stopping said container rotation foreffecting the collapse of said forced vortex.
 18. The method of claim 12wherein: said container is drum-like and rotatable on said axis which isgenerally vertical and includes a side wall generally coaxial with saidaxis, and wherein said rotation is effected generally horizontally aboutsaid axis.
 19. The method of claim 18 wherein the rotational velocity ofsaid drum-like container during said contact is a velocity at which thedistance between the substrate and the free surface of said forcedvortex is such that the Rayleigh Number is less than about
 1700. 20. Themethod of claim 19 wherein the solution contains immundities havingdensities greater than or less than the solution and wherein therotational velocity of said drum-like container during said contact is avelocity at which the denser immundities remain at the bottom of thecontainer and the less dense immundities float on said forced vortex outof contact with the substrate.
 21. The method of claim 18 wherein thesolution contains immundities having densities greater than or less thanthe solution and wherein the rotational velocity of said drum-likecontainer during said contact is a velocity at which the denserimmundities remain at the bottom of the container and the less denseimmundities float on said forced vortex out of contact with thesubstrate.
 22. The method of claim 18 which further includes the stepof: positioning the substrate within said drum-like container to beconstrained against vertical movement and radially movable horizontallytoward and away from said axis between a first and a second stop member,respectively.
 23. The method of claim 22 in which the substrate is lessdense than the solution and effectuation of the rotating step furtherincludes: contacting the substrate with the solution to move thesubstrate toward said axis and against said first stop member to exposea first surface thereof facing away from said axis and to impinge thesolution on said first surface.
 24. The method of claim 23 which furtherincludes the step of : surrounding the exterior of said drum-likecontainer with a first source of heat flux generally coaxial with saidaxis to orient said first surface at the cold end of the thermalgradient within the solution between sad first heat flux source and saidfirst surface.
 25. The method of claim 22 in which the substrate isdenser than the solution and effectuation of the rotating step furtherincludes: contacting the substrate with the solution to move thesubstrate away from said axis and against said second stop member toexpose a second surface thereof facing toward said axis and to impingethe solution on said second surface.
 26. The method of claim 25 whichfurther includes the step of: surrounding a second source of heat fluxwith said drum-like container, said second heat flux source beinggenerally coaxial with said axis to orient said second surface at thecold end of the thermal gradient within the solution between said secondheat flux source and said second surface.
 27. In a method of growing acrystal layer on a substrate from a heated, saturated solution rich in asolute made up of the crystal''s constituents, which method includescontacting the substrate with the solution, the solution includingimmundities having densities greater than or less than the solution, theimprovement comprising: a. placing the solution in an inner,fluid-receiving region of a drum rotatable on a major axis, the drumfurther including an outer annular region, both regions including sidewalls generally coaxial with said axis and interconnected at a positionabove the level of the solution within said inner region; b. positioningat least one substrate within said outer annular region; c. rotatingsaid drum until centrifugal action moves the solution in a first forcedvortex up said side wall of said inner region, through saidinterconnection, and into said outer annular region, to contact thesubstrate with a second forced solution vortex, such that the distanceof the substrate and the free surface of said second forced solutionvortex during said contacting is one whereby the Rayleigh Number is lessthan about 1700, the denser immundities remaining at the bottom of thesolution in said inner region, the less dense immundities floating onsaid first forced solution vortex at a level below said interconnection;and d. cooling the solution to effect growth of the crystal layer on thesubstrate by supersaturating the solution.
 28. The method of claim 27wherein step (b) includes: positioning the substrate within said outerannular region so that the substrate is constrained against verticalmovement and is radially movable horizontally toward and away from saidaxis between a first and a second stop member, respectively.
 29. Themethod of claim 28 in which the substrate is less dense than thesolution and effectuation of step (c) further includes: contacting thesubstrate with the solution to move the substrate toward said axis andagainst said first stop member to expose a first surface thereof facingaway from said axis and to impinge the solution of said second forcedvortex on said first surface.
 30. The method of claim 29 which furtherincludes the step of: surrounding the exterior of said drum with a firstsource of heat flux generally coaxial with said axis to orient saidfirst surface at the cold end of the thermal gradient within said secondforced solution vortex between said first heat source and said firstsurface.
 31. The method of claim 28 in which the substrate is denserthan the solution and effectuation of step (c) further includes:contacting the substrate with the solution to move the substrate awayfrom said axis and against said second stop member to expose a secondsurface thereof facing toward said axis and to impinge the solution ofsaid second forced vortex on said second surface.
 32. The method ofclaim 31 which further includes the step of: surrounding a second sourceof heat flux with said drum, said second heat source being generallycoaxial with said axis, to orient said second surface at the cold end ofthe thermal gradient within said second forced solution vortex betweensaid second Heat source and second surface.
 33. In a method of growing acrystal layer on a substrate comprising growing a crystalline layer upona selected surface of the substrate in a container from asuper-saturated solution containing the constituents of the layer, theimprovement comprising: forming the solution by centrifugal force into aforced vortex, comprising a substrate contacting layer, having athickness such that the Rayleigh Number is less than about 1700, whichcontacts the surface of the substrate.
 34. In a method of growing acrystal layer on a substrate, comprising growing a crystalline layerupon a selected surface of the substrate in a container from asupersaturated solution containing the constituents of the layer, theimprovement comprising: forming the solution by centrifugal force into aforced vortex having an immundity-free substrate contacting layer.
 35. Amethod of growing a crystal layer on a selected portion of a substratefrom a liquid body, rich in the constituents of the layer, theimprovement comprising: configurating the liquid body in a forcedvortex, and contacting the selected substrate portion with said forcedvortex such that any immundities present in the liquid body lie withouta region bounded by the distance between the selected substrate portionand said forced vortex.
 36. The method of claim 35 which includes thefurther step of: positioning the substrate in a container and whereinsaid configurating step includes: placing the liquid body in saidcontainer, and rotating the container.
 37. The method of claim 36wherein during said contacting step the rotational velocity of saidcontainer during said contact is a velocity at which the distancebetween the selected substrate portion and the free surface of saidforced vortex is such that the Rayleigh Number within said distance isless than about
 1700. 38. The method of claim 37 wherein said contactingstep is effected as a consequence of the effectuation of saidconfigurating step.
 39. In a method of growing a crystal layer on atleast a portion of a selected surface of a substrate in a container froma solution rich in a solute of the crystal''s constituents wherein (i) asolvent in the container out of contact with the substrate is saturatedat an elevated temperature with the solute to produce the solution, (ii)the selected substrate surface is contacted with the solution, and (iii)the solution is cooled to a supersaturated condition, the improvementcomprising: imposing on the solution a forced vortex configuration whichcontacts the selected substrate surface portion to effect step (ii) insuch a manner that any immundities contained in the solution lie withouta region bounded by the distance between the selected surface and thefree surface of said forced vortex.
 40. The method of claim 39 whereinsaid forced vortex is imposed on the solution by rotating the container.41. The method of claim 40 wherein the rotational velocity of thecontainer during said contact is a velocity at which the distancebetween the selected substrate surface portion and the free surface ofsaid forced solution vortex, measured generally perpendicular to saidselected substrate surface is such that the Rayleigh Number with saiddistance is less than about
 1700. 42. In a method of growing a crystallayer on a selected surface of a substrate in a container from asolution rich in a solute of the crystal''s constituents wherein (i) asolvent in the container out of contact with the substrate is saturatedat an elevated temperature with the solute to produce the solution, (ii)the selected substrate surface is contacted with the solution, and (iii)the solution is cooled to a supersaturated condition, the improvementcomprising: generating a forced vortex of the solution to cover theselected substrate surface therewith to effect step (ii) in such amanner that any immundities contained in the solution lie wiThout aregion bounded by the distance between the selected substrate surfaceand the free surface of said forced vortex.
 43. The method of claim 42wherein said forced vortex is generated by rotating the container. 44.The method of claim 43 wherein the rotational velocity of the containerduring said contact is a velocity at which the distance between theselected substrate surface and the free surface of said forced solutionvortex, measured generally perpendicular to said selected substratesurface is such that the Rayleigh Number without said distance is lessthan about
 1700. 45. In a method of growing a crystal layer on asubstrate in a container from a solution rich in a solute of thecrystal''s constituents wherein (i) a solvent in the container out ofcontact with the substrate is saturated at an elevated temperature withthe solute to produce the solution, (ii) the substrate is contacted bythe solution, and (iii) the solution is cooled until supersaturationoccurs, the improvement comprising: rotating the container on asymmetrical axis thereof at a sufficient rotational velocity to (1) movethe solution in a forced vortex which contacts the substrate to effectstep (ii), (2) effect retention at the bottom of the container of anyimmundities having a density greater than the solution and (3) effect afloating on said forced vortex out of contact with the substrate of anyimmundities having a density less than the solution.
 46. The method ofclaim 45 wherein step (iii) is effected after step (ii).
 47. The methodof claim 45 wherein step (iii) is effected before step (ii).
 48. Themethod of claim 45 wherein step (ii) and (iii) are effectedsimultaneously.
 49. The method of claim 45 which further includes thestep of: effecting relative movement between said forced solution vortexand the substrate for terminating the contact therebetween to terminatethe growth of the crystal layer.
 50. The method of claim 49 wherein saidrelative movement is effected by: stopping said container rotation foreffecting the collapse of said forced vortex.
 51. The method of claim 45wherein: said container is drum-like and rotatable on said axis which isgenerally vertical and includes a side wall generally coaxial with saidaxis, and wherein said rotation is effected generally horizontally aboutsaid axis.
 52. The method of claim 51 wherein the rotational velocity ofsaid drum-like container during said contact is a velocity at which thedistance between the substrate and the free surface of said forcedvortex is such that the Rayleigh Number is less than about
 1700. 53. Themethod of claim 51 which further includes the step of: positioning thesubstrate within said drum-like container to be constrained againstvertical movement and radially movable effectuation toward and away fromsaid axis between a first and a second stop member, respectively. 54.The method of claim 53 in which the substrate is less dense than thesolution and effectutation of the rotating step further includes:contacting the substrate with the solution to move the substrate towardsaid axis and against said first stop member to expose a first surfacethereof facing away from said axis and to impinge the solution on saidfirst surface.
 55. The method of claim 54 which further includes thestep of: surrounding the exterior of said drum-like container with afirst source of heat flux generally coaxial with said axis to orientsaid first surface at the cold end of the thermal gradient within thesolution between said first heat flux source and said first surface. 56.The method of claim 53 in which the substrate is denser than thesolution and effectuation of the rotating step further includes:contacting the substrate with the solution to move the substrate awayfrom said axis and against said second stop member to expose a secondsurface thereof facing toward said axis and to impinge the solution onsaid seconD surface.
 57. The method of claim 56 which further includesthe container, of: surrounding a second source of heat flux with saiddrum-like container said second heat flux source being generally coaxialwith said axis to orient said second surface at the cold end of thethermal gradient within the solution between said second heat fluxsource and said second surface.
 58. In a method of growing a crystallayer on a substrate from a heated, saturated solution rich in a solutemade up of the crystal''s constituents, which method includes contactingthe substrate with the solution, the solution including immunditieshaving densities greater than or less than the solution, the improvementcomprising: a. placing the solution in an inner, fluid-receiving regionof a drum rotatable on a major axis, the drum further including an outerannular region, both regions including side walls generally coaxial withsaid axis and interconnected at a position above the level of thesolution within said inner region; b. positioning at least one substratewithin said outer annular region; c. rotating said drum untilcentrifugal action moves the solution in a first forced vortex up saidside wall of said inner region, through said interconnection, and intosaid outer annular region, to contact the substrate with a second forcedsolution vortex, the denser immundities remaining at the bottom of thesolution in said inner region, the less dense immundities floating onsaid first forced solution vortex at a level below said interconnection;and d. cooling the solution to effect growth of the crystal layer on thesubstrate by supersaturating the solution.
 59. The method of claim 58wherein step (b) includes: positioning the substrate within said outerannular region so that the substrate is constrained against verticalmovement and is radially movable horizontally toward and away from saidaxis between a first and a second stop member, respectively.
 60. Themethod of claim 59 in which the substrate is less dense than thesolution and effectuation of step (c) further includes: contacting thesubstrate with the solution to move the substrate toward said axis andagainst said first stop member to expose a first surface thereof facingaway from said axis and to impinge the solution of said second forcedvortex on said first surface.
 61. The method of claim 60 which furtherincludes the step of: surrounding the exterior of said drum with a firstsource of heat flux generally coaxial with said axis to orient saidfirst surface at the cold end of the thermal gradient within said secondforced solution vortex between said first heat source and said firstsurface.
 62. The method of claim 59 in which the substrate is denserthan the solution and effectuation of step (c) further includes:contacting the substrate with the solution to move the substrate awayfrom said axis and against said second stop member to expose a secondsurface thereof facing toward said axis and to impinge the solution ofsaid second forced vortex on said second surface.